Micro injection fuel/air premixer/combustion

Lean premixed (LP) combustion has become the dominant industrial approach to reduce NOx emissions. Homogeneous mixing of lean fuel and air mixtures prevents the presence of undesirable localized regions of near-stoichiometric fuel/air mixtures, thereby allowing a reduction in thermal NOx. A new concept, a multi-point micro injection premixer, is presented in this dissertation. The multi-point micro injection premixer is a porous plate that provides a simple but extremely effective method to mix air and fuel. An array of fuel jets is injected in a direction perpendicular to the plane of the premixer plate into an oncoming counterflow stream of air. The fuel mixes with the air, and reverses direction. The mixture of air and fuel travels back through the injector plate exiting as an extremely uniform mixture. A simplified numerical model was built to analyze the case of a single micro counterflow jet mixing into on an oncoming air stream. The model predicted that a higher fuel/air momentum ratio results in better mixing. Four injection plates are fabricated with different combinations of hole arrays and hole diameters. The velocity measurement by constant temperature anemometer showed that all jets in a premixer have similar jet velocity profiles. Velocity profiles were taken near the dump plane of the combustor for a variety of cases. It was found that the presence of the premixer plate had very little effect on the macroscopic velocity distribution. However, with counter-injection, the turbulence intensity was much greater across the core region exiting the premixer, and less near the periphery (compared to the case without counter-injection). From combustion experiments, it is found that at same fuel and air mass flow rates, the cases where a micro injector was used to mix air and fuel produced lower equivalence ratio at LBO, higher heat release rate and lower NOx emission than the cases without counter injection. Furthermore, the higher the counterflow jet velocity, the better the combustion performance. From all the experiment data it is shown that the new concept multi-point micro injection premixer provides very good mixing of fuel/air with high efficiency